This disclosure is related to the field of reflection seismic data acquisition. More specifically, the disclosure relates to methods for acquiring seismic data that include measurement related to a vertical particle motion wavefield gradient transverse to the vertical direction in order to interpolate the detected wavefield between seismic sensor positions.
Marine seismic data is known in the art to be acquired through measurements of pressure in response to actuation of a seismic energy source using sensors such as hydrophones disposed at longitudinally and laterally spaced apart locations along a plurality of laterally separated marine streamers towed behind a survey vessel. More recently, marine seismic data has been acquired using both pressure or pressure time gradient measurements and measurements of particle motion, particle acceleration or particle velocity using co-located pressure and motion responsive sensors, e.g., hydrophones and geophones in marine streamers as described above. Obtaining both pressure and particle motion signals from a seismic wavefield enables, e.g., separation of wavefield direction of motion with respect to the sensors, and as a result up-going and down-going wavefields can be distinguished and separated from detected seismic signals.
More recently, marine seismic data acquisition systems have been introduced which measure a horizontal gradient of the pressure wavefield (see, e.g., U.S. Pat. No. 8,521,437 issued to Moore). Measuring the horizontal pressure wavefield gradient enables further improved understanding of the detected wavefield. Using the measured horizontal wavefield gradient it is possible, for example, to reconstruct the full wavefield at locations where measurements were not made, e.g., between seismic sensor positions along a streamer, or between adjacent streamers. While pressure gradient measurement is readily performed in a marine environment, where the acoustic medium in which the sensors is disposed (water) is essentially homogeneous, and gradient measurement of the pressure can be made relatively easily, devices which measure the horizontal gradient of the vertical particle velocity, particle acceleration or particle motion wavefield have not been used.
Onshore (i.e., land-based) seismic data is typically acquired using geophones (velocity sensitive detectors) or other particle motion responsive sensors disposed in a selected pattern proximate the ground surface. Geophones may be arranged to make a single vertical component measurement at each sensor location, or alternatively, measurements of both vertical and horizontal particle motion, acceleration or velocity measurements may be made with three-component geophones which separately measure velocity in three (typically mutually orthogonal) directions. However, three component, single position velocity or particle motion measurements do not provide measurements usable to determine the horizontal gradient of the vertical particle motion (or acceleration or velocity) wavefield.